1. Field of the Invention
This invention relates to a microcomputer having a central processing unit (hereinafter called "CPU"), a memory and a peripheral function unit or the like integrally formed on a semiconductor substrate. The present invention particularly relates to a technique providing access to a peripheral function unit of a memory mapped I/O type microcomputer wherein a memory and the peripheral function unit are disposed in the same address space.
2. Description of the Related Art
A conventional microcomputer is one wherein a CPU, a memory comprising a Read Only Memory (hereinafter called "ROM") and a Random Access Memory (hereinafter called "RAM"), and a peripheral function unit having a timer, an analog-to-digital (hereinafter called "A/D") converter, a parallel input/output portion, a series input/output portion, etc. have been formed on a single semiconductor substrate. This microcomputer is called "one-chip microcomputer". The CPU, the memory and the peripheral function unit are electrically connected to one another by an address bus, a data bus and a control bus common to them. The CPU, the memory and the peripheral function unit are disposed within the same address space and provides an address system referred to as a so-called memory mapped I/O type.
In this type of memory mapped I/O type microcomputer, the same memory reference instruction as that used for access to the memory is used for read/write access to the peripheral function unit. Further, the microcomputer is activated in the same timing as that provided for the memory.